The concept of wage slavery goes way back.
Cicero wrote in his De Officiis that
whoever gives his labor for money sells himself and puts himself in the rank of slaves.
and comparing wage slaves with chattel slaves
In 1763, the French journalist Simon Linguet published a description of wage slavery:
The slave was precious to his master because of the money he had cost him . . . They were worth at least as much as they could be sold for in the market . . . It is the impossibility of living by any other means that compels our farm labourers to till the soil whose fruits they will not eat and our masons to construct buildings in which they will not live . . . It is want that compels them to go down on their knees to the rich man in order to get from him permission to enrich him . . . what effective gain [has] the suppression of slavery brought [him ?] He is free, you say. Ah! That is his misfortune . . . These men . . . [have] the most terrible, the most imperious of masters, that is, need. . . . They must therefore find someone to hire them, or die of hunger. Is that to be free?[17]
http://en.wikipedia.org/wiki/Wage_slavery